Church Father’s writing you can use:
“If any one confesses Christ Jesus the Lord, but denies the God of the law and of the prophets, saying that the Father of Christ is not the Maker of heaven and earth, he has not continued in the truth any more than his father the devil, and is a disciple of Simon Magus, not of the Holy Spirit.” Ignatius of Antioch, To the Philadelphians, 5 (A.D. 110).
“…Christ Jesus, our Lord, and God, and Saviour, and King, according to the will of the invisible Father, ‘every knee should bow, of things in heaven, and things in earth, and things under the earth, and that every tongue should confess’ to Him, and that He should execute just judgment towards all; that He may send ‘spiritual wickednesses,’ and the angels who transgressed and became apostates, together with the ungodly, and unrighteous, and wicked, and profane among men, into everlasting fire; but may, in the exercise of His grace, confer immortality on the righteous, and holy, and those who have kept His commandments, and have persevered in His love, some from the beginning of their Christian course, and others from the date of their repentance, and may surround them with everlasting glory.” Irenaeus, Against Heresies, 1,10,10 (A.D. 180).
"…thus also the punishment of those who do not believe the Word of God, and despise His advent, and are turned away backwards, is increased; being not merely temporal, but rendered also eternal. For to whomsoever the Lord shall say, ‘Depart from me, ye cursed, into everlasting fire,’ these shall be damned for ever; and to whomsoever He shall say, “Come, ye blessed of my Father, inherit the kingdom prepared for you for eternity,’ these do receive the kingdom for ever, and make constant advance in it; since there is one and the same God the Father, and His Word, who has been always present with the human race, by means indeed of various dispensations, and has wrought out many things, and saved from the beginning those who are saved, (for these are they who love God, and follow the Word of God according to the class to which they belong,) and has judged those who are judged, that is, those who forget God, and are blasphemous, and transgressors of His word.” Irenaeus, Against Heresies, 4,28,2 (A.D. 180).
“But do you also, if you please, give reverential attention to the prophetic Scriptures, and they will make your way plainer for escaping the eternal punishments, and obtaining the eternal prizes of God.” Theophilus of Antioch, To Autolycus, 1:14 (A.D. 181).
“[T]hese have further set before us the proofs He has given of His majesty in judgments by floods and fires, the rules appointed by Him for securing His favour, as well as the retribution in store for the ignoring, forsaking and keeping them, as being about at the end of all to adjudge His worshippers to everlasting life, and the wicked to the doom of fire at once without ending and without break, raising up again all the dead from the beginning, reforming and renewing them with the object of awarding either recompense.” Tertullian, Apology, 18:3 (A.D. 197).
“Therefore after this there is neither death nor repeated resurrections, but we shall be the same that we are now, and still unchanged–the servants of God, ever with God, clothed upon with the proper substance of eternity; but the profane, and all who are not true worshippers of God, in like manner shall be consigned to the punishment of everlasting fire–that fire which, from its very nature indeed, directly ministers to their incorruptibility.” Tertullian, Apology, 48:12 (A.D. 197).
“[T]he world when thou shall know what it is to live truly in heaven, when thou shalt despise that which is here esteemed to be death, when thou shalt fear what is truly death, which is reserved for those who shall be condemned to the eternal fire, which shall afflict those even to the end that are committed to it.” Letter to Diognetus 10:7 (A.D. 200).
“Of which voice the justification will be seen in the awarding to each that which is just; since to those who have done well shall be assigned righteously eternal bliss, and to the lovers of iniquity shall be given eternal punishment.” Hippolytus, Against the Greeks, 3 (ante A.D. 225).
“Oh,what and how great will that day be at its coming, beloved brethren, when the Lord shall begin to count up His people, and to recognize the deservings of each one by the inspection of His divine knowledge, to send the guilty to Gehenna, and to set on fire our persecutors with the perpetual burning of a penal fire, but to pay to us the reward of our faith and devotion!” Cyprian, To Thibaris, Epistle 55 (58):10 (A.D. 253).
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